In order to maintain paved thoroughfares, such as roadways, runways, ramps, walkways, sidewalks, parking lots, etc. clear from snow and ice, deicers such as sodium chloride and traction enhancers such as sand, either singly or in combination, are applied to the surface. The objectives being to melt the frozen water by depressing its melting temperature and/or provide a tractive medium over the slippery thoroughfare. Under non-extreme conditions, sodium chloride is generally sufficient to melt snow and ice.
Typically, sand, cinders, stone, chips, etc. are added to the salt in varying ratios to enhance the capabilities of the treatment material.
Other compounds have been substituted for sodium chloride with varying degrees of success. Examples include calcium chloride, magnesium chloride, potassium chloride, magnesium acetate, calcium acetate and calcium magnesium acetate.
These agents must be physically applied to the roadway on a periodic basis. Road traffic, plowing and the physical melting of the snow and ice inexorably remove the agents from the area being treated thereby reducing the effectiveness of the treatment. As a consequence, repeated applications of the materials with the attendant fiscal and environmental costs are required.
In an attempt to overcome problems associated with repeated applications of deicing materials, the Iowa Department of Transportation placed an experimental asphaltic concrete overlay containing an ice retardant additive called Verglimit.RTM. consisting primarily of deicing salts and sodium hydroxide over an existing road. The results are set forth in the bulletin entitled "Ice-Retardant Pavement", Research Project HR290, November 1991.
The results were apparently disappointing. Due to the hydrophilic nature of the material, the road surface became slippery since it tended to retain surface moisture. "Because of the problems with wetting of the pavement surface during periods of high humidity, the limited climatic conditions under which the ice-retardant overlay performs, it[s] limited deicing potential and it[s] high cost, it is doubtful the City of Des Moines would place an[o]ther ice-retardant overlay"--Page 9.